The present invention relates to an electromechanical transducer which may be applied, for example, to a helical scan type videotape recorder (VTR) to displace a magnetic head thereof into alignment with a magnetic track on a videotape. The present invention also relates to a control device for such a transducer.
Prior art electromechanical transducers of the type described include a bimorph which has two piezoelectric elements bonded together, each of the piezoelectric elements carrying electrodes at either side thereof. The bimorph suffers from the drawbacks that its frequency characteristic involves many resonances and antiresonances, and that the linearity attainable therewith is poor due to hysteresis characteristic. Therefore, damping has to be applied to the bimorph in order to control it.
One approach heretofore proposed to meet the demand described above is bonding rubber or like pads to the bimorph to mechanically effect damping. Another approach known in the art is electrical and consists in sensing a position or a velocity of the bimorph by some method, and applying negative feedback to the input after signal processing. The mechanical and electrical approaches have been combined for some applications.
The mechanical damping scheme relying on pads limits the available displacement of the bimorph due to the pads which are fit on the bimorph itself. This will cause the displacement amplitude to become critically small when sufficient damping is effected on the bimorph. The electrical damper, on the other hand, requires an intricate circuit arrangement therefor even if combined with the mechanical damper, because the bimorph involves many resonances and antiresonances.